The Citizens are taking on Real in the round of 16 of the competition, with much of their season resting on the outcome.
City are already out of reach in the Premier League, which means the Champions League is their main chance of having a successful season.
And Toure wishes they had gotten an easier draw.
"But we will see - the first game is at the Bernabeu and then it is [at the] Etihad.
"I'm a little scared to be honest."